In the event of an emergency such as an earthquake and a typhoon, a number of local residents are often obliged to live together in an evacuation center, etc. In such a case, disposal of excrement is an unavoidable problem. In such an emergency, procurement of a large number of small-sized mobile toilets is often difficult from the standpoints of cost, transportation, etc. Even if this is successful, an installation site having a given area is necessary. To overcome this problem, there has been proposed a collapsible toilet (collapsible arched portable toilet) that can be prepared in advance and poses few limitations on the installation site. As shown in FIGS. 14 and 15, a portable toilet S is made of cardboard having a plurality of division lines (fold formation lines) given in advance, and can be formed into an arch shape by folding the board along the division lines in a predetermined order (Patent Document 1).